1. Field of the Invention
The present invention relates to enhancing the security of machines which must be periodically opened for routine service and, particularly, to increasing the difficulty of obtaining unauthorized access to the interior of machines which include a cache of currency. More specifically, this invention is directed to a lock for use in the vending industry and, especially, to an improved "plug lock" which may be installed in a T-handle of a vending machine or the like. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in the vending industry. Many "vending" machines, and as used herein the term "vending machine" includes machines which collect a fee and/or make change, are provided with a T-handle which is employed to gain access to the interior of the machine for, by way of example, restocking. Such T-handles are fabricated from a high strength material and, in the normal operating position, are seated in a complementary shaped recess in the housing or outer casing of the associated machine. The T-handle has a tubular shaft portion, which opens through the cross-member, which receives a lock cylinder, i.e., a "plug lock". The T-handle shaft, in turn, is received in a tubular housing and the latch member of the lock engages an aperture in this housing in the locked state. When the plug lock is operated to the unlocked position, by means of a properly bitted key, the latch member will be disengaged from the housing and the thus released T-handle will be driven out of its recess by a biasing spring. The operator, gaining access to the T-handle, may then rotate the handle thereby causing a screw threaded extension rod coupled to the shaft thereof to become disengaged from a complementary threaded receiver located within the machine. When the rod is fully disengaged from the receiver, the access door to the machine may be opened.
Two different types of plug lock have previously been installed in T-handles of vending machines. A first type of prior art plug lock is basically a spring loaded latch mechanism which allows the operator to employ a key to unlock the device and then remove the key. When the door is closed, the latch member may be reengaged with a receiver in the housing simply by pushing the T-handle to its final recessed, i.e., normal locked, position without reinsertion of the key. This ability to lock the machine without the use of a key is a convenience and generally ensures that service personnel will not accidentally leave the machine unlocked. The described self-latching ability results from the fact that the spring biased latch member can be depressed when the cylinder of the plug lock is in either the locked or unlocked state. Such latch type plug locks, however, present a significant security problem. That is, latch-type plug locks can be defeated simply by drilling a small hole in the machine, inserting a stiff wire through the drilled hole and unlocking the machine by using the wire to depress the latch even though the cylinder is in the locked state.
The other type of previously employed "plug lock" utilizes a deadlocking bolt in lieu of the spring latch. A deadlocking bolt has the obvious advantage that, when the cylinder is in the locked position, the bolt cannot be depressed, i.e., the bolt can only be disengaged by using a properly bitted key. While the use of a deadlocking bolt affords enhanced security against defeat by surreptitious means, as discussed above, it requires deliberate locking with a key when the access door is closed and the T-handle pushed into its receiving recess. This is an inconvenience and presents the potential for inadvertent failure to relock. For example, in the case of a badly worn locking mechanism, it is possible for the T-handle to appear to be in the locked position even though the deadlocking bolt has not been engaged through operation of the key.